We plan to study in vitro the conditions that regulate the levels of membrane expression of IgM and IgD on single cells. The effects of treatment with antibodies againt IgD allotypes will be studied in Fl hybrids; the basic theme here will be that of detecting the effects of the anti-IgD treatment on the number of plasma cells containing and secreting IgG or IgA molecules marked by the allotypes in "cis" of "trans" position with regard to the target IgD allele. These effects will be studied in mice treated with anti-IgD either from birth (suppressed for one IgD allele) or for short term in adult life. We are also going to study the cellular expression of different isotypes of the mouse anti-dextran alpha 1 3 system with particular attention to the genetic control of this expression and to the effect of anti-idiotypes.